Variational analysis of LCVD rod growth

Variational analysis of LCVD rod growth was made possible by a new axial convection enhanced micro-reactor design that lent itself to accurate in-process measurements of growth rate and position inside the growth region. The methodology follows a typical design of experiments approach where the effect of small perturbations to process parameters are measured in real-time. The findings are rather startling. They point to a growth rate that is not symmetrical with respect to the focal plane. In fact, the peak growth rate is consistently recorded well in front of the focal plane, at a distance one order of magnitude greater than the Raleigh range, decreases rapidly afterward, steadies across the focus, and then decreases slowly. A measure of energetic efficiency can be derived that shows a rapid decay of the amount of material deposited per Joule. A central assumption to this analysis is that growth occurs in the kinetic domain and that was confirmed experimentally. The reason for the great variability and asymmetry observed are still unknown. However, corroboration of our results would throw into question a large body of published LCVD measurements as they would have to account for the wide variability of the measured quantities within the growth region. PACS 81.16.Mk; 81.10.Bk; 81.05.Uw